Hydraulic drive systems are employed on a variety of machines to perform various tasks. Many of the tasks require linear actuators or hydraulic motors. The linear actuators are often double acting and therefore require two hydraulic lines. The hydraulic motors all require a hydraulic fluid supply line and a hydraulic return line.
The machines that have hydraulic actuator systems have a pump driven by a power source and may have multiple attachments that are changed from time to time. To change from one attachment to another, hydraulic quick couplers have been developed. Hydraulic quick couplers generally include a male portion and a female portion. Both portions generally have check valves that close when they are disconnected. These check valves close to prevent the loss of hydraulic fluid and to reduce contamination of the hydraulic systems. Fine sand, dust, and liquid contaminants will cause serious damage to hydraulic systems and shorten their useful life. The check valves automatically close when the couplers are disconnected. Both check valves are open when the couplers are connected.
The male coupler portion of a hydraulic coupler is relatively easy to clean. The female coupler portion of a hydraulic coupler is somewhat more difficult to clean. Plugs can be used to help keep the female coupler portion clean when not in use. The general practice employed in most hydraulic systems is to attach the female coupler portion directly to a control valve. The control valve is connected to the pump that supplies hydraulic fluid under pressure and to a sump. The female coupler portion is generally in use when the pump is in use. The male coupler is generally connected to the actuator or motor on a device that is to receive and to be driven by hydraulic fluid. The male couplers occasionally sit for periods of time unused.
The male coupler portion is often connected to a closed system when it is disconnected from the female coupler portion. The closed system will contain some hydraulic fluid. The closed system may even be pressurized if there is an actuator in the system that is loaded. Hydraulic fluid is substantially uncompressable. However, the volume of most hydraulic fluids change with changes in temperature. A temperature increase of the hydraulic fluid in a closed system can increase the pressure to the point that the male coupler portion can not be manually connected to a female coupler portion. In order to couple the male coupler portion to a female coupler portion, some hydraulic fluid under pressure may have to be released from the closed system. If an actuator in the closed system is supporting a load, it can be necessary to drain a quantity of hydraulic fluid from the system.
During the release of hydraulic fluid under pressure from any hydraulic system, care must be taken to avoid contact with high velocity streams of fluid as well as hot fluids and cold fluids. Fluids release from a pressurized system can penetrate a person's skin, if moving at a high velocity, and cause injury.